With the advent of active and passive MMIC technology, there is an increasing interest for developing integrated high millimeter-wave (MMW) and terahertz systems for applications in ultrafastwireless communication and short-range miniature radars for navigation and imaging. The short wavelength at these frequency bands enables the integration of antennas and other waveguide-based passive components such as couplers and filters with MMIC active modules to develop fully integrated communication links and radar front-ends. These waveguide based components have been implemented on silicon wafers using micromachining technology. On the other hand, active MMIC modules are typically implemented on planar transmission lines. Hence, a reliable transition from on-wafer waveguides to planar transmission lines is essential to realize fully integrated systems.
A number of transition approaches from planar transmission lines to rectangular waveguide using microfabrication technology for W-band and higher frequencies have been reported in the literature. All of these transitions have complex 3-D geometries which require assembly of various parts. Considering the dimensions in sub-MMW and terahertz region, implementation of such transitions with acceptable accuracy becomes very difficult. Hence, fully micromachined transitions which do not require assembly of parts are preferred for these high frequency applications. A 2.5-D fully micromachined resonant-based transition has been proposed. In this design, the transition is realized using two resonant structures: a shorted section of transmission line with a pin inside the waveguide and an E-plane step discontinuity. However, due to the resonant nature of the transition, the fractional bandwidth is limited to 17%. In addition, the performance of the transition is sensitive to good contact with the shorting pin and the waveguide step height which are subject to micromachining tolerances.
Microstrip-to-rectangular waveguide transitions using the impedance-tapering technique have been reported in the literature. In these structures, a multistep ridged-waveguide impedance taper is typically used to convert the quasi-TEM mode on the microstrip line to the TE01 mode in the rectangular waveguide. However, the particular geometry of these designs where the ridged section extends over the planar transmission line (i.e., microstrip) cannot be easily fabricated by micromachining where both the waveguide ceiling and the planar transmission line are at same level (wafer's top surface). Hence, for high-frequency applications, this disclosure presents a novel impedance taper transition is proposed which is compatible with silicon micromachining.
This section provides background information related to the present disclosure which is not necessarily prior art.